The present invention relates to a method of making a mandrel comprising a drill section for constructing a self-drilling blind rivet.
The prior art "self-drilling blind rivet" comprises a tubular rivet body and an elongated mandrel inserted through the rivet body. The elongated mandrel has at its one end a drill section capable of self-drilling an object in which the blind rivet is to be attached. The drill section has an outer diameter comparatively greater than that of the tubular rivet body. However, there has not been offered any effective method to mass produce such a drill section at the end of the elongated mandrel. Consequently, a great demand for this type of blind rivet has not been met with a sufficient supply.
To met this demand, Japanese Patent Laying-Open Gazette Hei. 2-197347 and corresponding to U.S. Pat. No. 4,998,853 propose a method wherein a short drill tip is adjoined or welded to one end of a mandrel.
This previous method has however proved not necessarily satisfactory due to a certain difficulty in ensuring an coaxial relationship between each mandrel and each drill tip joined thereto. Thus, the mass production of the blind rivet according to the proposed method has not been realized, because a specially designed automatic welder is required, which welder is not presently available.